Lithographic process using a stop bath



Aug. 25, 1964 K. L. WRISLEY ETAL 3,146,105

LITHOGRAPHIC PROCESS USING A STOP BATH Filed NOV. 15, 1962 EXPOSURE r I27 W V EMULSION DEVELOPING AGENT Y ALKALINE ACTIVNION, STOP BAITLINKINGSUPPORT Fig.

EMULSION OGGED) Ems/m ALKALINE ACTIVATION, STOP BATH "wakeKennelhLwp-isleg WillialnE.Gulhrie 1N VENTORS United States Patent3,146,105 LITHOGRAPHIC PROCESS USING A STOP BATH Kenneth L. Wrisley andWilliam E. Guthrie, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey Filed Nov. 15, 1962, Ser. No. 237,837 16 Claims. (Cl.%-33) This invention concerns photographic lithographic printing platescomprising a silver halide photographic emulsion containing a developingagent and, more particularly, a stop bath for use in processing theselithographic printing plates.

In U.S. patent application Serial No. 861,125, filed December 21, 1958,in the names of Yackel and Abbott, is disclosed a photographic methodfor preparing lithographic printing plates which involves the formationof a developable silver halide image, as by means of exposure to a lineor halftone subject, of a hydrophilic organic colloid-silver halidefilm, such as a gelatino-silver halide sensitized plate, followed bysilver halide development.

The exposed plates are normally developed in an alkaline activator andthen placed in an acid stop bath before being placed on the printingpress or offset duplicator. In our invention, we have found that theaddition of benzyl alcohol to the acid stop bath improves thelithographic differcntiation of the plate by making the background morewater-receptive without affecting the ink receptivity of the image. Thismakes the plate less susceptible to scumming or background inking whenit is used on the printing press.

One object of this invention is to provide a process for obtaining aphotographic lithographic printing plate having improved resistance toscumming. Another object is to provide an improved acid stop bath forprocessing lithographic printing plates. An additional object is toprovide a process for improving the lithographic dilferentiation of theplate by making the background more water-receptive without affectingthe ink-receptivity of the image. Additional objects will be apparentfi'om the following disclosure.

The above objects are obtained by using a stop bath containing benzylalcohol along with a solvent for the benzyl alcohol and an acid such asphosphoric acid.

The following concentrated stop bath formula gives our preferredcomposition:

Percent by weight Benzyl alcohol 14.0 Triethylene glycol 72.8 Phosphoricacid (85%) 13.2

This formulation is a concentrated form which is diluted with water tomake a working solution as required for the particular photographicplate to be processed. Dilution of this concentrate to about 1:8 withwater is recommended as a good working solution.

The benzyl alcohol is the critical component of the stop bath and can bevaried between about 1 to by weight of the working stop bath solutiondepending upon the printing conditions. Additional levels of benzylalcohol can be used above 10% by weight of the solution, but if theconcentration becomes too high, blinding of the printing plate willresult.

The triethylene glycol serves as a solvent for the benzyl alcohol butany common solvent for benzyl alcohol and water can be used in an amountnecessary to solubilize the benzyl alcohol. An excess of the commonsolvent can be used without impairing the operating effectiveness of thestop bath. For instance, other common solvents which can be used includeethyl alcohol, 2-ethoxyethanol, and the like. It will be appreciatedthat since there is a large number of common solvents, a listing ofevery common solvent here would not be practical.

Although phosphoric acid is the preferred acid, it will be appreciatedthat other acids can be used which have similar properties with respectto dissociation constant, such as acetic acid, glycolic acid, citricacid, etc. The amount of acid may be from 1 to 10% by weight of theworking solution.

In the accompanying drawings representative sensitive elements of theprocess are shown in greatly enlarged cross-sectional views at variousstages of the preparation of lithographic printing plates.

In FIG. 1 a negative-positive process is illustrated and in FIG. 2 isshown a positive-positive process.

In FIG. 1, layer 10 of the element of Stage 1 represents a support suchas paper, film base, etc., layer 11 is a hydrophilic agent and aquantity of black colloidal silver or carbon black, etc., forantihalation protection, layer 12 a gelatino-silver halide emulsionlayer for recording the line or halftone image.

In the process of FIG. 1, after exposure to a subject as shown in area13, followed by alkaline activation, stop bath, and inking, the elementappears substantially as shown in Stage 2, area 14 being composed ofsilver and the reaction product of the oxidized developing agent and thehydrophilic organic colloid present in the silver halide emulsion layerproduced in the development reaction, carrying the ink image 15, theundeveloped area 16 of layer 12 remaining hydrophilic and repellent ofprinting ink when moistened with water.

In FIG. 2 is shown a positive-positive system in Stage 1 of which theelement includes a support 20 such as a paper or film support, layer 21an antihalation hydrophilic colloid layer containing developing agentand black colloidal silver, carbon black, etc., layer 22 a hydrophilicorganic colloid silver halide emulsion layer, and layer 23 a foggedsilver halide emulsion layer. Upon image exposure in region 24 followedby alkaline activation, stop bath and inking, the element appearssubstantially as shown in Stage 2, the silver halide developing agent oflayer 21 which has not been utilized in developing the negative silverimage in area 24 of layer 22 having developed a positive silver halideimage to silver in areas 25 of layer 23. The ink images 26 are acceptedin areas 25 which are composed of silver and the reaction product of thehydrophilic organic colloid present in the silver halide emulsion layerand the oxidized developing agent. The remaining areas 27 arehydrophilic and repel printing ink when the plate is moistened in thelithographic printing press.

In the sensitive elements described, the emulsion layers should besubstantially hardened, particularly the outermost emulsion layer, e.g.,layer 12 of FIG. 1 and layer 23 of FIG. 2, in order to prevent thealkaline activated, stopped and inked emulsions from adhering toprinting blankets, printing paper, etc. For this purpose the emulsionshould be as hard as a gelatin layer containing at least about 2 gramsand preferably from about 2 to 15 grams of dry formaldehyde per pound ofgelatin.

In the preferred arrangement, the developing. agent is incorporated in aseparate layer under the silver halide emulsion layer since thisarrangement gives improved sharpness, latitude and better quality inkimages than when the developing agent is incorporated directly in theemulsion layer.

The following examples are intended to illustrate our invention but notto limit it in any way.

Example 1 The element of Example 1 of US. Serial No. 861,125, filedDecember 21, 1959, was exposed to a line negative,

:3 then activated for 20 seconds in a 4 percent solution of sodiumcarbonate monohydrate.

The film was placed in a 2 percent phosphoric acid stop bath for 20seconds and then placed on a Model 1250 Multilith Duplictor using VanSon, ink and Repelex fountain solution.

The resulting printed copy had considerable scum in the backgroundareas.

A duplicate photographic printing plate prepared employing the stop bathdisclosed above in our preferred embodiment, diluted to contain about 2%phosphoric acid for 20 seconds and run on the same duplictor with thesame ink and fountain solution gave printed copy which had a crisp blackimage and no traces of background scumming.

Example 2 The element of Example 2 of US. Ser. No. 861,125 was exposedand processed as described in Example 1.

A 2% phosphoric acid stop bath was used and considerable trouble withscum was encountered on the printed copies using AddressographMultigraph ink, ML-36 and the Repelex fountain solution. A stop bathhaving our preferred formulation diluted to contain about 2% phosphoricacid was substituted for the phosphoric acid stop bath and the printedcopy from the photographic plate treated in this manner showed no scumproblem. This process with the same formulation of the improved stopbath was used for a period of five weeks without encountering anyscumming problem.

Example 3 The sensitive element of Example 3 of US. Ser No. 861,125 wasexposed to a line positive, processed 60 seconds in 4 percent aqueoussodium carbonate monohydrate solution, treated in a 2 percent aqueousacetic acid stop bath for 1 minute and squeegeed to remove excessliquid.

This plate was used on a A. B. Dick Duplicator using A. B. Dick 21010ink and Repelex fountain solution. Considerable scum was encountered inthe resulting prints. A duplicate print was then prepared and processedas above employing our preferred embodiment diluted to contain about 2%phosphoric acid as the stop bath. No scum was encountered.

The Repelex fountain solution used in this invention is disclosed in VanDusen US. Patent 2,393,875, issued January 29, 1946.

Many treatments are known to improve ink-water differentiation andprevent scumming on litho plates. Pretreatment of the plate with an acidsolution of acetamide has been used to increase the hydrophilicity ofthe plate. Scumming of inks, particularly those with slow dryingcharacteristics, can often be prevented'by the addition of ethyleneglycols or polyglycols such as Carbowax 600 to the inks used forlithographic printing. Fountain solutions are sometimes modified withformamide to prevent scumming. When the stop bath of our invention isused, such modification of the ink or solutions is not necessary.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. A concentrated photographic stop bath for use with lithographicprinting plates comprising about 14% by weight benzyl alcohol, about 13%by weight phosphoric acid, and about 73% by weight triethylene glycol.

2. A photographic stop bath for use with lithographic printing platescomprising an aqueous solution and between about 110% by weight benzylalcohol, about 1- by weight of an acid selected from the classconsisting of phosphoric acid, acetic acid, glycolic acid and citricacid, and a water miscible organic solvent.

3. A photographic stop bath for use with lithographic printing platescomprising an aqueous solution and between about 110% by weight benzylalcohol, about 1- 10% by weight of phosphoric acid, and a water miscibleorganic solvent.

4. A photographic stop bath for use with lithographic printing platescomprising an aqueous solution and between about 110% by weight benzylalcohol, about 1 10% by weight of acetic acid, and a water miscibleorganic solvent.

5. A photographic stop bath for use with lithographic printing platescomprising an aqueous solution and between about 1-10% by weight benzylalcohol, about 1- 10% by weight of glycolic acid, and a water miscibleorganic solvent.

6. A photographic stop bath for use with lithographic printing platescomprising an aqueous solution and between about 110% by weight benzylalcohol, about 1- 10% by weight of citric acid, and a water miscibleorganic solvent.

7. The process of producing a lithographic printing plate from anexposed photographic element comprising a support having thereon agelatin layer containing therein a silver halide developing agentcapable of oxidation in the presence of a hydrophilic organic colloid toform an image receptive to greasy printing ink, and over said gelatinlayer on exposed hydrophilic organic colloid silver halide emulsioncontaining a hardener, in which the colloid has a hardness equivalent tothat of a gelatin layer containing from about 2 grams to about 15 gramsof dry formaldehyde per pound of gelatin, comprising:

(1) initiating the development of the exposed emulsion layer with analkaline solution, thereby forming an image, and

(2) arresting the developing action by means of an aqueous solutioncontaining 1-10% by weight benzyl alcohol, about 110% by weight of anacid selected from the class consisting of phosphoric acid, acetic acid,glycolic acid and citric acid and an organic water miscible solvent.

8. The process of claim 7 in which the acid is phosphoric acid.

9. The process of claim 7 in which the acid is acetic acid.

10. The process of claim 7 in which the acid is glycolic acid.

11. The process of claim 7 in which the acid is citric 7 acid.

12. The process for producing a silver image in an exposed photographicelement comprising a support having thereon in order, a first layercomprising a silver halide developing agent capable of oxidation in thepresence of a hydrophilic organic colloid to form an image receptive togreasy printing inks, a second layer comprising an exposed hydrophilicorganic colloid silver halide emulsion and the third layer comprising afogged hydrophilic organic colloid silver halide emulsion containing ahardener, in which the colloid has a hardness equivalent to that of agelatin layer containing from about 2 grams to about 15 grams of dryformaldehyde per pound of gelatin, comprising:

(1) initiating the development of the exposed sensitive element with analkaline solution thereby forming a negative image in the second layerand a positive image in the third layer resulting from the migration tothe third layer of the unused silver halide developing agent present inthe unexposed areas of the second layer, and

(2) arresting the developing action by means of an aqueous solutioncontaining 110% by weight benzyl alcohol, about 110% by weight of anacid selected from the class consisting of phosphoric acid, acetic acid,glycolic acid and citric acid, and a water rniS- cible organic solvent.

References Cited in the file of this patent UNITED STATES PATENTS BrusonApr. 24, 1945 Yackel et al Aug, 19, 1952 Kimura et a1 May 27, 1958Wendell Feb. 3, 195-9 Kimura et al Apr. 18, 1961

7. THE PROCESS OF PRODUCING A LITHOGRAPHIC PRINTING PLATE FROM ANEXPOSED PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT HAVING THEREON AGELATIN LAYER CONTAINING THEREIN A SILVER HALIDE DEVELOPING AGENTCAPABLE OF OXIDATION IN THE PRESENCE OF A HYDROPHILIC ORGANIC COLLOID TOFORM AN IMAGE RECEPTIVE TO GREASY PRINTING INK, AND OVER SAID GELATINLAYER ON EXPOSED HYDROPHILIC ORGANIC COLLOID SILVER HALIDE EMULSIONCONTAINING A HARDENER, IN WHICH THE COLLOID HAS A HARDNESS EQUIVALENT TOTHAT OF A GELATIN LAYER CONTAINING FROM ABOUT 2 GRAMS TO ABOUT 15 GRAMSOF DRY FORMALDEHYDE PER POUND OF GELATIN, COMPRISING: (1) INITIATING THEDEVELOPMENT OF THE EXPOSED EMULSION LAYER WITH AN ALKALINE SOLUTION,THEREBY FORMING AN IMAGE, AND (2) ARRESTING THE DEVELOPING ACTION BYMEANS OF AN AQUEOUS SOLUTION CONTAINING 1-10% BY WEIGHT BENZYL ALCOHOL,ABOUT 1-10% BY WEIGHT OF AN ACID SELECTED FROM THE CLASS CONSISTING OFPHOSPHORIC ACID, ACETIC ACID, GLYCOLIC ACID AND CITRIC ACID AND ANORGANIC WATER MISCIBLE SOLVENT.